1. Field of the Invention
This invention relates to a liquid jet head which performs recording by discharging liquid for recording ink, etc. utilizing heat energy to form droplets and attaching such droplets onto a recording medium such as paper, as well as to a substrate for the head and a liquid jet recording apparatus equipped therewith.
2. Related Background Art
A recording for the liquid jet recording method which utilizes heat energy for formation of a droplet to be discharged generally comprises a base plate having an opening for discharging liquid; a liquid path communicated to said discharging opening having a portion at which heat energy for discharging the liquid is generated by an electro-thermal transducer and a pair of electrodes connected to said heat-generating resistor. The head may have, for example, a structure shown in the schematic exploded perspective view in FIG. 2.
Among the recording heads having such constitution, for example, are the recording heads disclosed in Japanese Laid-open Patent Publication Nos. 55-128467 and 59-194866, which as shown in FIG. 1, comprise a substrate 202 a heat-generating resistor 208 for generating heat energy, electrodes 209 and 210 for supplying electrical signals thereto and protective layers 213 and 214 laminated thereon for protection from liquid and are formed according to thin film forming technique, etc. The recording head comprises a liquid path 204 corresponding to the heat generating portion 201 of the heat-generating resistor 208 and a discharging outlet 217 formed on the substrate.
The first protective layer 213 of the above protective layers 213 and 214 primarily insulates between the electrodes 209 and 210, while the second protective layer 214 surfaces liquid resistance and mechanical strength.
As the material for forming the second protective layer 214, there have been known in the art noble metals, (elements of the group VIII, etc.), high melting transition elements (elements of the groups III, IV, V, VI, etc.), alloys of these, or nitrides, borides, silicides, carbides of these metals or amorphous silicon, etc.
The useful life of the recording head having a protective layer on the heat-generating resistor described above depends greatly on the performance of the protective layer on the heat-generating portion of the heat-generating resistor.
That is, since the protective layer is subject to the heat which gas lies the liquid and thus, the cavitation shock created during droplet discharging and chemical action of liquid, it must breaking, liquid and oxidation resistance, etc.
However, no material for formation of protective layer satisfying all of these requirements, particularly for formation of second protective layer, has been known in the art.
For example, in the protective layer comprising nitrides, borides, silicides or carbides of the above metals sometimes feature the drawback of weak resistance to mechanical shock by cavitation shock, which may be due to the covalent atomic bonds of such compounds.